Specification 9 Cavity barriers for fire-protected timber

This Specification sets out requirements for cavity barriers in fire-protected timber construction.

(1) Cavity barriers must be provided in the following locations where fire-protected timber is used in any of the listed elements:

1. At concealed cavities adjacent to junctions between fire-resisting floor/ceiling assemblies and fire-resisting walls.
2. At concealed cavities adjacent to junctions between fire-resisting floor/ceiling assemblies and fire-resisting or non-combustible external walls.
3. At concealed cavities adjacent to junctions between fire-resisting walls and fire-resisting or non-combustible external walls.
4. Around the perimeter of door and window openings in fire-resisting construction.

(2) Cavity barriers must be installed so they are tight fitting and are able to withstand thermal expansion and structural movement without the loss of seal against fire and smoke.

(3) In addition to cavity barriers required by (1), horizontal and vertical cavity barriers are to be provided to wall cavities within, around or adjacent to fire-protected timber elements as follows:

1. Horizontal cavity barriers — at not more than 5 m centres.
2. Vertical cavity barriers — at not more than 10 m centres.

(4) Cavity barriers must—

1. achieve the performance specified in Table S9C2 based on the highest FRL of the elements they are mounted within or seal against; or
2. consist of—
   1. timber with the minimum thickness specified in Table S9C2; or
   2. polythene-sleeved mineral wool or mineral wool slabs or strips placed under compression to achieve the minimum thickness specified in Table S9C2.

(5) Cavity barriers provided around openings may be formed by the window or door frame if—

1. the frame is constructed of steel or timber with the minimum thickness specified in Table S9C2 for timber; and
2. the frame is tightly fitted to rigid construction and mechanically fixed in position.

(6) The FRL of cavity barriers in fire-protected timber construction must be determined in accordance with Specifications 1 and 2 applying the criteria for control joint systems specified in Section 10 of AS 1530.4 with the cavity barrier system fitted within an opening between timber members exposed directly to the furnace heating conditions.

(7) Notwithstanding anything to the contrary in Specifications 1 and 2 or AS 1530.4, the test results from (6) may be used when the fire-protected timber is constructed from timber having a nominal density at least equal to the tested timber.